Lab 12: GUI programming with Qt

Transcription

1 Lab 12: GUI programming with Comp Sci 1585 Data Structures Lab: Tools for Computer Scientists

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4 (Pronounced cute ) is used for developing multi-platform s and graphical user interfaces (GUIs) So far, we ve only created command-line s GUIs can be nice at times, though : cross-platform framework (works on Windows, Mac OS X, Linux, etc) Little to no underlying changes needed to port from one system to another Native OS capabilities and speed

5 Making GUIs with 4 Besides making clickable programs, learning to program GUIs will give you several other skills with C++ Event-based programming Working with a (very) large library Managing memory in more complicated programs

6 Getting Started #include <Gui> int main(int argc, char *argv[]) { QApplication app(argc, argv); QLabel hello("hello World!"); hello.resize(250, 150); hello.setwindowtitle(" example"); hello.show(); } return app.exec();

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8 Building Applications has its own preprocessor, the Meta Object Compiler (aka moc ) qmake-qt4 manages projects and generates makefiles automatically $ qmake-qt4 -project will make a project file (ends in.pro) that configures the makefile $ qmake-qt4 makes a makefile So, to build a project: $ qmake-qt4 -project; qmake-qt4; make

9 Overview There is one, and only one, QApplication qapp is a global pointer to the QApplication Everything clickable is called a widget Widgets can hold other widgets A widget with no parent becomes a window

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11 A Notepad #include<qapplication> #include<qtextedit> int main(int argc, char** argv) { QApplication app(argc,argv); QTextEdit te; te.setwindowtitle("not Vim"); te.show(); return app.exec(); }

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13 Composite Objects Widgets can be added to another widget with the addwidget() function You can use a Layout to specify how the widgets are organized Memory Management: addwidget() takes a pointer and is responsible for cleaning up all its children

14 Layout Example #include<gui> int main(int argc, char** argv) { QApplication app(argc,argv); QTextEdit* te = new QTextEdit; QPushButton* quit = new QPushButton("&Quit"); QVBoxLayout* layout = new QVBoxLayout; layout->addwidget(quit); layout->addwidget(te); QWidget window; window.setlayout(layout); window.show(); return app.exec(); }

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16 Making Buttons Do Things is event-driven: QApplication monitors what the user does and sends events to widgets when something happens Signal: An event caused by a widget: button click, key press, etc. Slot: An action taken when a signal is sent Signals are connected to slots by using the connect(...) function e.g. connect(source-object, SIGNAL(signal name()), destination-object, SLOT(slot name())) connects signals to slots

17 Actually Quitting #include<gui> int main(int argc, char** argv) { QApplication app(argc,argv); QTextEdit* te = new QTextEdit; QPushButton* quit = new QPushButton("&Quit"); QObject::connect(quit, SIGNAL(clicked()), qapp, SLOT(quit())); QVBoxLayout* layout = new QVBoxLayout; layout->addwidget(quit); layout->addwidget(te); QWidget window; window.setlayout(layout); window.show(); return app.exec(); }

18 Writing your own slot In order to make your own slots, you need to make a custom QWidget class In addition to public and private functions and members, QObjects have public and private slots A slot is just a function that gets called whenever a signal connected to it is sent Example: ask-quit

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20 Toolbars QMainWindow is a class for making standard s with menus and setcentralwidget() sets the widget that fills the window menubar() returns a pointer to the menubar, which you can use to add new menus addtoolbar() creates a new toolbar To avoid repeating a lot of code, you can add a QAction to both a menu and a toolbar Then you can connect that one action to various slots Example: menus

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22 Sending Data Between Signals and Slots So far, we ve used predefined signals e.g. QPushButton::clicked() e.g. QAction::triggered() connect() dictates which signals trigger which slots e.g. openaction::triggered() executes Notepad::open() Custom slots were responsible for gathering data Notepad::open() promped user to select file Grabbed filename Tried to open; complained if it couldn t Loaded file contents into QTextEdit instance Another approach: have signals send data to slots Solution: declare your own signals!

23 Sending Data Between Signals and Slots You can declare your own signals in the signals: section of your header files Then, custom slots can emit these signals: emit signal-name(); You don t actually implement signals, just declare, emit, and connect them Signals can carry data, just add parameters Connect that signal to a slot that takes the same arguments The slot will be called with the data you use when you emit the signal Example: title

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25 -creator makes an IDE for developing s: